Elevated brain levels of iron and aluminum in patients with Alzheimer's disease suggest that these metals play a role in the disease process. One mechanism for this action is in the production of reactive oxygen species (ROS), or oxygen free radicals. If the production of ROS exceeds the cellular protective mechanisms, ROS will destructively oxidize many cell constituents, including enzymes. The proposed work will focus on the effect of ROS on an important metabolic enzyme in brain energy metabolism, lactate dehydrogenase (LDH). We found in some preliminary experiments that ascorbate plus iron inactivates LDH in a way that suggests ROS are involved. The experimental model to be used for studying enzyme inactivation in iron systems is an in vitro model; LDH is incubated with iron and ascorbate and the decrease in LDH activity is a measure of chemical damage to the enzyme. Ascorbate can be a protective antioxidant, but under some conditions it can contribute to oxidative damage by way of Fe3+ reduction to Fe2+. Fe2+ can act in two ways to catalyze the production of ROS; 1) it can react with O2 to form superoxide radical, and 2) it can react with hydrogen peroxide to produce the highly reactive hydroxyl radical. The specific aims are: 1) To know whether or not the iron/ascorbate inactivation of lactate dehydrogenase (LDH) is largely the result of reactive oxygen species, and if so, which species are involved. 2) To know the ascorbate/iron concentration relationships that cause greatest enzyme inactivation. 3) To find if protein-bound iron, in addition to iron salts, can produce enzyme inactivation in the presence of ascorbate. The protein-bound forms to be studied are human heme protein, transferrin and ferritin. 4) To determine if the addition of aluminum or lead salts to the ascorbate/iron/LDH system potentiates LDH inactivation.